Jonas Platt (June 30, 1769 Poughkeepsie, New York, Dutchess County, New York – February 22, 1834 Peru, Clinton County, New York) was an American lawyer and politician from New York. He was a member of the United States House of Representatives.
Jonas Platt was the son of Zephaniah Platt, who founded Plattsburgh, New York. He attended a French Academy at Montreal, Canada, studied law, and was admitted to the bar in 1790. He married Helena Livingston (1767–1859), sister of John Henry Livingston), and they had eight children, among them Michigan Attorney General Zephaniah Platt (1796–1871).
He practiced law in Poughkeepsie and served as the county clerk of Herkimer County, New York, from 1791 to 1798. He was also the county clerk of Oneida County, New York, from 1798 to 1802. He was a member of the New York State Assembly in 1796.
Platt was elected as a Federalist to the Sixth Congress, and served from March 4, 1799, to March 3, 1801. He was the chairman of the United States House Committee on Revisal and Unfinished Business. Afterward, he resumed the practice of law and served as a general in the Cavalry in the New York State Militia. In 1810, he was an unsuccessful candidate for governor. He was a member of the New York State Senate from 1810 to 1813. He was also a member of the Council of Appointment in 1813.
- Jonas Platt at the Biographical Directory of the United States Congress
-  Livingston family tree
|United States House of Representatives|
|Member of the U.S. House of Representatives
from New York's 9th congressional district